Spin and activity of comet 67P/Churyumov-Gerasimenko

Abstract

Aims. In 2014 ESA's spacecraft Rosetta will reach its final target: comet 67P/Churyumov-Gerasimenko (67P). Although this comet has been studied in great detail over the past decade, there are still some uncertainties regarding the actual spin orientation and the distribution of active regions on the surface. We here give an overview of our current knowledge of these critical parameters based mainly on data acquired during the last orbit of the comet aims to deliver a review of what is our current knowledge of these critical parameters. Methods. We based our analysis on the modeling and interpretation of dust jets seen in the coma of 67P during the 2009 apparition.Results. The inversion of ground-based images leads to an estimate of the spin axis orientation (RA = 40• ± 10 • , Dec = 70 • ± 10 • ) and to the localization of the most prominent active areas on the surface of the nucleus. We can reproduce the activity with three active regions localized at −45• , 0• , and +60• of latitude. We use these results to revisit the observations taken during the 2003 apparition and examine the changes in activity between then and now. Our model from 2009 is also valid for the 2003 data, which suggests that no significant change in spin orientation and active areas occurred from one perihelion passage to the next. Finally, we combine all the results to propose some predictions on the activity to be expected in 2015 during the comet exploration phase of the Rosetta mission.

Beginning of activity in 67P/Churyumov-Gerasimenko and predictions for 2014–2015

“…The idea that 67P reaches its peak in activity shortly after perihelion is in agreement with past results based on water production rate (Schleicher 2006) and coma morphology (Vincent et al 2013). Lightcurves based on amateur photometry around perihelion also show this asymmetry (Kidger 2003;Ferrín 2005), with the peak occurring approximately one month after perihelion.…”

“…in crater-like depressions) that only see sunlight near to perihelion (and hence produce a boost in activity at this time). Vincent et al (2013) use such a seasonal model to explain the relative strengths of jets seen in the coma. Observations by Rosetta will allow us to differentiate between these various effects.…”

“…Further image processing reveals jets within the coma, which are seen to change in strength around the orbit. Agarwal et al (2007) and Vincent et al (2013) discuss the large scale and fine structure morphology of the comet in detail. Tozzi et al (2011) found that A f ρ varied with ρ for observations of 67P at r = 2.3 AU pre-perihelion, and so the coma did not behave as 1/ρ.…”

“…As the comet passed through aphelion its inactive nucleus was studied by Tubiana et al (2008Tubiana et al ( , 2011 and Lowry et al (2012), before it was observed in an active state again as it returned to perihelion in 2008 (Tozzi et al 2011;Lara et al 2011). Further authors have studied the longer lived dust trail associated with the comet (Ishiguro 2008;Kelley et al 2008;Agarwal et al 2010), the dust's polarisation (Hadamcik et al 2010), the nucleus thermal properties (Kelley et al 2006;Lamy et al 2008;Kelley et al 2009), and the morphology (Vincent et al 2013) and composition (Schleicher 2006) of its coma over multiple apparitions.…”

Geomorphology of the Imhotep region on comet 67P/Churyumov-Gerasimenko from OSIRIS observations

“…These particular illumination conditions and overall geomorphology render Imhotep a good candidate for being an active region when approaching perihelion (Keller et al 2015). This point is further reinforced by the observations of Vincent et al (2013), who suggested the equatorial region as the source of the strongest jet observed on 67P close to perihelion. Finally, Imhotep may be representative of the regions of the southern hemisphere that have not yet been illuminated and imaged, but will exit polar night in March 2015 and be fully illuminated at perihelion in August 2015.…”